A substantial portion of the world's oil reserves comprise bitumens, which are sometimes referred to as tar sands, and heavy crude oils (collectively “heavy oil”). Heavy oil is difficult to produce, and, when produced, is difficult to market. Whether pipelines or shipping facilities are used as the transportation medium, the cost of transporting heavy oil is substantially higher than the cost for the transporting of light oil. Once heavy oil is delivered at a receiving refinery, more costly refinery processes are required to generate products suitable for the commercial marketplace. As a result, the economic value of heavy oil is lower than the value of light oil, and for that reason a significant percentage of the world's heavy oil reserves remain underutilized.
To alleviate this underutilization problem, numerous methods have been proposed to upgrade heavy oil. Although the terms “heavy oil” and “upgrade” can be defined using several different technical parameters, one parameter that is frequently used to characterize the quality of hydrocarbons is API gravity. Heavy oil is characterized by a generally low API gravity, for example but without limitation in the range of API 5 to API 25. Light oils have higher magnitude API gravities, for example in the range API 35 to API 50. The term “upgrade” refers to the process of increasing the API gravity of oil from a relatively lower API gravity to a relatively higher API gravity. For example, but without limitation, oil can be upgraded from API 5 to API 15, or from API 30 to API 40. Upgrade is a relative term, and is not limited to a specific initial API gravity value, or range, nor to a specific final API gravity value, or range. Finally, the phrase “heavy oil upgrade reaction” refers generically to the chemical activities that occur in the process of upgrading heavy oil.
Heavy oil upgrade methods sometimes involve pre-processing steps intended to increase the efficiency of the heavy oil upgrade reaction. For example, U.S. Pat. No. 4,294,686 discloses the preliminary distillation of the heavy oil stream into a light oil fraction and heavy oil fraction. The purpose of the preliminary distillation is to avoid the unwanted cracking and coking of the light oil fraction that might occur if that fraction were included in the input stream to the upgrade reactor. The light oil fraction that results is generally in a form satisfactory either for use in the production facility as a fuel or for transport to a refinery. However, preliminary distillation adds both cost and complexity to the overall upgrade process, and is useful only where the heavy oil is known to include a sufficient volume of light hydrocarbons.
Other proposed upgrade methods include the pre-processing step of mixing of an oil additive with the heavy oil. The resulting mixture is then input to an upgrade reactor. For example, U.S. Pat. No. 6,059,957 discloses the creation of an emulsion from the mixing of heavy oil and water. That disclosure also provides for the optional inclusion of an emulsion-stabilizing surfactant. U.S. Pat. No. 6,004,453 discloses the creation of a slurry from the mixing of a noncatalytic additive with the heavy oil. The publication of Moll, J. K. and Ng, F.T.T., “A Novel Process for Upgrading Heavy Oil/Bitumen Emulsions Via In Situ Hydrogen,” 16th World Petroleum Congress, Calgary, Canada, June 2000, discloses use of an emulsion from a water-soluble dispersed catalyst. Each of these three methods has two general limitations however. First, the mixing step adds both cost and complexity to the overall upgrading process. Second, the additives cause the creation of waste materials during the upgrade reactions that must thereafter be appropriately processed and disposed. That processing and disposal also adds cost and complexity.
A third set of heavy oil upgrade methods include the step of using a reaction additive in the upgrade reactor to facilitate, or improve the efficiency of, the upgrade reaction. For example, the publication of Paez, R., Luzardo, L., and Guitian, J., “Current and Future Upgrading Options for the Orinoco Heavy Crude Oils,” 16th World Petroleum Congress, Calgary, Canada, June 2000, discloses the use of coke or iron-based catalysts in the upgrading process. Disclosure WO 00/61705 discloses the use of a non-catalytic particulate heat carrier. U.S. Pat. No. 5,817,229 discloses the use of activated carbon, in the absence of added hydrogen, to both reduce the content of undesirable minerals and to upgrade the quality of the input crude. These methods have both of the limitations of the oil additive methods discussed above, namely added cost and complexity and increased waste material processing requirements.
The hydrogenation method of U.S. Pat. No. 5,069,775 reacts hydrogen and heavy oil for from five minutes to four hours in a preferred reaction temperature range of 800 to 900° F. (427 to 482° C.). U.S. Pat. No. 5,269,909 discloses a method whereby a gas rich in methane is reacted with heavy oil for at least thirty minutes in a preferred temperature range of 380 to 420° C. (716 to 788° F.). The method of U.S. Pat. No. 5,133,941 flows hydrogen and heavy oil through sequentially connected reaction passageways in a preferred temperature range of 700 to 900° F. (371 to 482° C.). As will be understood to those skilled in the art, a limitation of these methods is that the generally long reaction durations cause a substantial increase in the generation of undesirable waste materials, specifically pitch, coke, and olefins. These materials create significant disposal challenges for the processing facility, and, in addition, lead to a reduction in the efficiency of the facility.
Disclosure WO 00/18854 discloses a two-part process in which hydrogen gas is mixed with heavy oil in a manner that attempts to achieve molecular level dispersion of hydrogen throughout the heavy oil. The method has a first upgrade reaction that separates the lighter hydrocarbons from the heavy oil, and continues with a second upgrade reaction in a second reactor. The second upgrade reaction further upgrades the heavy oil via a hydrogenation reaction within a preferred temperature range of 343 to 510° C. (650 to 950° F.). The method includes the added step of providing externally supplied heat to the hydrogen-heavy oil mixture to further facilitate the reaction in the second reactor. Limitations of this process include the difficulty of achieving the required uniform mixing of hydrogen and heavy oil, and the cost and complexity of implementing a process that requires two reaction steps.
These and other previously proposed upgrade methods suffer from an inherent limitation that has long plagued industry. On one hand, it is well known to those skilled in the art that upgrade reactions are preferably carried out at the highest possible reaction temperature, since upgrade processes are more efficient at higher temperatures. Unfortunately, as is also well known to those skilled in the art, high reaction temperatures can lead to significant unwanted cracking and coking of the heavy oil molecules if the reactions are not quickly quenched. None of these methods have a mechanism for quickly quenching the reactions and they are therefore constrained to lower temperature operating ranges. On the other hand, however, reaction durations are longer at lower temperatures, and it is equally well known that long reaction also lead unwanted cracking and coking, and, in addition, to lower process efficiencies due to the extra time required for the upgrade. These methods are therefore constrained to a compromise temperature range that is a tradeoff between these limitations.
WO 00/23540 discloses a method in which a jet of gas, comprising essentially of superheated steam, activates the upgrading of the heavy oil. The method has a number of limitations. Using steam as the hydrogenation mechanism means that both hydrogen and oxygen-hydrogen radicals are generated in the upgrade reactions. As a result, fewer hydrogen molecules are available, in comparison to processes in which hydrocarbon-based gases are predominantly used, to saturate the carbon radicals created from the heavy oil carbon bond breaking. In addition, a large volume of superheated steam is required. Because steam generation is endothermic, this constraint is costly, self-limiting, and inherently inefficient—fuel is consumed to generate steam, but the energy in that steam is only passively used to provide a thermal input to the upgrading of the heavy oil. Thus energy losses are incurred both in the generation of the steam and in the passive upgrade. This limits the efficiency of the upgrading process.
Another limitation of WO 00/23540 is that the bonding of oxygen-hydrogen radicals from the steam with carbon radicals from the heavy oil creates an output product in an emulsion form. Emulsions are a less desirable product at refineries due to the need to handle the increased volume of produced water that results during the refining process. Emulsions also add the requirement for a post-reaction soaking drum to ensure stabilization of the output products. Because soakers cannot quickly quench upgrade reactions or actively control stabilization times, this limitation leads to the creation of pitch and other unwanted waste materials.
Finally, WO 00/23540 is also constrained by the use of steam as the predominant hydrogenation source for the upgrade reaction. Steam causes side reactions that cannot be completely inhibited except under a narrow range of pressure and temperature conditions. Outside that range, unwanted gases and waste products are generated, and the output product suffers a loss of stability. As a result, reaction temperatures are generally limited to 500° C. (932° F.) or less, another efficiency constraint.
It is apparent that a need exists for a method that can be carried out without a preliminary distillation step, and without the use of oil or reaction additives. The method should avoid unwanted cracking and coking of the heavy oil, and minimize the production of undesirable waste materials. The output product should not be an emulsion. The upgrade efficiency of the method should not require uniform dispersion of hydrogen or other input gas throughout the heavy oil, or require relatively long exposure durations of the input gas to the heavy oil.
Furthermore, a need exists for a method that can preferably be carried out at high temperatures, to thereby facilitate short reaction times and high upgrade efficiencies. The method should involve a direct mechanism of transferring the heat input to the heavy oil to be upgraded. The method should include an active mechanism for quickly quenching the upgrade reactions. The present invention satisfies these requirements.